1. Field of the Invention
The present invention relates to metal cutting, and more particularly, to high-energy thermal melting or plasma cutting devices that cut patterns in metal.
2. Brief Description of the Prior Art
Metal workpieces cart be thermally cut by a plasma cutting torch on a plasma cutting table. The workpiece is first placed on an X-Y coordinate table, with X representing a longitudinal distance of the table and Y representing a lateral distance of the table. The table is typically fashioned as a hollow grid, such as a mesh or honeycomb design. Specifically, the grid is a plurality of solid metal bars or beams forming geometrically-shaped orifices between these members. A plasma cutting torch is then positioned adjacent a top surface of the workpiece, directly opposite a portion to be cut. Plasma cutting torches ionize a column of gas with an electric arc, producing a high velocity, high temperature plasma stream. When a plasma stream strikes the workpiece, the heat instantly melts a desired portion of the workpiece away while the high-velocity stream blows the molten metal through the orifices in the table. In one prior art table, the molten metal, commonly referred to as slag, is directed by a hopper into a slag cart positioned adjacent a second surface of the table. Such an arrangement is generally disclosed in U.S. Pat. No. 4,063,059 to Brolund et al.
In addition to the slag, the ionized gas and molten metal create gaseous vapors which must be evacuated. To solve the problem of evacuating the gaseous vapors, some prior art devices have vacuum hoses positioned adjacent either the plasma torch or in a slag cart. The vacuum hoses are connected to vacuum pumps. Spark boxes, positioned between the vacuum hoses and vacuum pumps, help prevent the filtration of hot slag and gases into the vacuum pumps.
When cutting a workpiece, either the workpiece can be moved while the plasma cutting torch stays fixed, or the plasma cutting torch and hopper can move while the workpiece stays fixed. Since workpieces can be very heavy, moving the plasma cutter torch and hopper is a preferred method. However, because the plasma torch must be able to reach every point on a surface of a workpiece, the accompanying vacuum hoses must also be long enough to reach any point on the table. For example, if the plasma torch moves two feet in an X direction along the table, at least two additional feet of vacuum hose is needed. Moreover, such a table must be divided into zones, with electric or mechanical dampers in each zone. The long hose lengths are unwieldy and potentially unsafe. The hoses and dampers increase the maintenance cost of the plasma cutting torch table. Therefore, there exists a need for a plasma cutting torch table which eliminates unwieldy vacuum hoses and electronic and mechanical dampers.